1. Field of the Invention
The present invention relates to an image forming apparatus which controls a fixing operation for heating, pressing and fixing a toner image formed by a copier, a printer or the like to a recording medium.
2. Description of the Background
An image forming apparatus, such as an electrophotographic copier, printer or facsimile, includes a fixing device to heat, press and fix a toner image on a recording medium. As a system of the fixing device as stated above, there is a heat roller system in which a recording medium on which a toner image is formed is made to pass through a nip formed in a press contact part between a heat roller and a press roller, and the toner image is heated, pressed and fixed.
On the other hand, in recent years, there is growing awareness of environmental regulation or environmental protection. Thus, hitherto, there is an image forming apparatus in which power is supplied to a heat member only at the time of image formation, and when the image formation is not performed, power supply to a heat source of a heat roller is cut off, and energy saving is realized. However, in the image forming apparatus as stated above, although reduction in power consumption can be obtained, in a case where the heat capacity of the heat roller is large, at the time of image formation, the heat roller can not be immediately raised to a printable surface temperature (fixing temperature) and there is a fear that a long heating time is required before the image formation is started.
Thus, there is also an apparatus in which when image formation is not performed, a so-called preheat mode is held in which a heat roller is made to have a preheat temperature slightly lower than a printable temperature, and at the time of image formation, the heat roller can be immediately raised to the usable temperature. However, for further energy saving, it is also desired to save the consumption of power in the preheat mode.
Thus, hitherto, JP-A-2002-184554 discloses an image forming apparatus in which at the time of standby of an image formation operation, power is not supplied to a heat unit and the power is saved, and at the time of start of heating of the heat unit, a large capacity of power is supplied from both a main power source and an auxiliary power source device to raise the heat unit up to a specified temperature in a short time. However, since the auxiliary power source device is generally expensive, even if it takes a long time to raise the heat unit, some users do not desire to purchase the auxiliary power source device.
Then, an image forming apparatus is desired in which a user's option can be widened according to various user's desires in purchase conditions of the image forming apparatus, conditions of image formation function, and the like.